Added an additional master TOC index for Bro script packages that
automatically gets filled in at ``make doc`` time. The master TOC
links to per-package indexes which contains links to all the scripts
contained within it along with their summary. The per-package index
is also now automatically generated/derived from the path component
of the script passed into the rest_target() macro.
It's now all implemented in CMake scripting.
The generation of reST docs is now a distinct target, "restdoc", while
the target to generate HTML docs, "doc", depends on "restdoc". reST doc
generation supports incremental builds (documentation for a given policy
script is only regenerated when it is out of date), but HTML doc generation
via ``make doc`` is not incremental (Sphinx always starts with fresh input).
Building the "restdoc" target is now covered by a btest to ensure all
policy scripts are parse-able when Bro is in "doc mode".
Generated reST docs should now support "@load"ing from subdirectories. e.g.
"@load foo/baz" and "@load bar/baz" will now generate the right xref links.
